Where should I write this function?

As per this link :
http://www.dotnetfunda.com/articles/article808-how-to-write-a-simple-login-page-in-aspnet.aspx
In the above Stored Procedure we count the Records that have matched the Records and if there is one record found then it is a good login else it is a bad login. But how will you use this in your asp.net Page. First we have to create a Function that will access the stored procedure and call that function in click event of the button. Create a Function as show below in your page not inside your page load because you will get an Error.
public int Validate_Login(String Username, String Password)
{
SqlConnection con = new SqlConnection(@"User id=sa;Password=Dotnetfunda;Server=VUYISWA\VUYISWA;Database=Forum");
SqlCommand cmdselect = new SqlCommand();
cmdselect.CommandType = CommandType.StoredProcedure;
cmdselect.CommandText = "[dbo].[prcLoginv]";
cmdselect.Parameters.Add("@Username", SqlDbType.VarChar, 50).V ...